key: cord-0747224-e98r6e8c
authors: Chan, Edward Wai Wa; Leung, Miriam Tim Yin; Lau, Lauren Ka Wun; Leung, Janice; Lum, Dawn; Wong, Rosa Sze-Man; Li, Xue; Chui, Celine Sze Ling; Wan, Eric Yuk Fai; Wong, Carlos King Ho; Chan, Esther Wai Yin; Ip, Patrick; Wong, Ian Chi Kei; Lai, Francisco Tsz Tsun
title: Comparing self-reported reactogenicity between adolescents and adults following the use of BNT162b2 (Pfizer-BioNTech) messenger RNA Covid-19 vaccine: a prospective cohort study
date: 2021-12-26
journal: Int J Infect Dis
DOI: 10.1016/j.ijid.2021.12.354
sha: bd7f6da12eb7ddb6f7e866bd7676d2b1bd741463
doc_id: 747224
cord_uid: e98r6e8c

Objectives Although clinical data have shown that the BNT162b2 vaccine, which is widely used in many countries, is safe and effective as a protection against the Covid-19 infection, extant research in adverse reactions using real-world data of various socio-demographic characteristics is scant. Methods We conducted a prospective cohort study to compare age differences in self-reported reactogenicity of BNT162b2 in Hong Kong. A total of 1,516 participants were intensively followed up for two weeks following both doses of BNT162b2 vaccination, during which their basic demographic, health conditions, and medication information were collected. Results Results from generalized mixed model showed that compared with adults aged 18 – 59, older adults aged 60 or above had a lower risk of adverse reactions, and adolescents aged 12 – 17 had a moderately higher risk. Conclusions Results of this study should be informative to parents considering BNT162b2 vaccination for their children in that moderately increased reactogenicity compared with adults is anticipated.

 Marked age differences in adverse reaction risks from BNT162b2 vaccination  Moderately increased risks from BNT162b2 in adolescents compared to adults  Self-reported adverse reactions peaked on first follow-up day after vaccination The BNT162b2 messenger RNA Covid-19 vaccine, widely used in more than 100 countries worldwide, has been shown to be safe and effective in protecting populations from the infection of SARS-CoV-2 (Polack et al., 2020; Thomas et al., 2021; Walsh et al., 2020) .

According to clinical trial data, more than 80% of BNT162b2 recipients reported postvaccination adverse reactions such as pain and tiredness, although an extremely small proportion of these reactions required medical interventions (Polack et al., 2020) . Current research seldom examined such adverse reactions in sub-populations of various socio-demographic characteristics, however.

Since the emergency use of BNT162b2 in adolescents aged 12 or above has been approved in an increasing number of jurisdictions worldwide with few substitutes (Frenck et al., 2021) , its self-reported reactogenicity as compared to adult recipients in real-world settings should be examined to better inform parents' decision to permit their children to receive the vaccine (Musa et al., 2021) . This study aimed to assess the potential risk differences in the selfreported reactogenicity of BNT162b2 among adolescents, middle-aged adults, and older adults. METHODS A prospective cohort design with self-reported data was adopted for this study. Data were collected on the first-dose vaccination day as baseline. Participants were then followed up on the first, second, third, seventh, and the fourteenth day following both doses of vaccination. Basic demographic, health conditions, and medication information were collected during baseline and any self-report adverse reactions were collected throughout the observation period*. Generalized linear mixed model was performed to examine the association between age group and self-reported adverse reactions † , adjusting for person-level and measurement-level covariates ‡ . Listwise deletion was applied for missing data due to its relatively negligible proportion. Odds ratios and confidence intervals were obtained for comparisons of risks between the trichotomized age groups (adolescents 12-17 years; middle-aged adults 18-59 years; and elderly 60 years or above) at .05 significant level by R (version 4.1.1).

As of 12 th August 2021, we recruited 2,531 participants (1,016 aged 12-17 years, 759 18-59 years, and 756 60 years or above) who had received BNT162b2. The follow-up success rates of our study were 90.6%, 96.7%, and 72.0% for the adolescent, middle-aged adult, and older adult groups respectively. Details of cohort characteristics are shown in Table 1 .

[Insert Table 1 (Frenck et al., 2021) , there has been little existing research reporting the reactogenicity of BNT162b2 in adolescents in the literature. A plausible explanation of the observed age differences is that, consistent with previous research evidence (Woudenberg et al., 2021) , the immune response triggered by a viral infection or vaccines in individuals of a younger age is typically stronger than in those of an older age.

Study limitations that need to be taken into consideration include the design of serial selfreport online survey, which entails a risk of omitting the follow-up survey of who had more serious adverse reactions and required medical interventions or were even hospitalized, as evidenced by the imperfect response rates. Self-report bias may also exist in the reactogenicity data, which might partially be induced by the educational gap across the age groups.

The results of this study should be informative to parents considering BNT162b2 vaccination for their children in that moderately increased reactogenicity compared with adults is anticipated, and that severe adverse reactions are rare. Considering the entirety of the existing body of knowledge about the reactogenicity and adverse events following the use of BNT162b2, we believe the benefits of receiving the vaccine still far outweigh the associated risks. Findings should inform the choice of vaccine uptake for parents of eligible adolescents. Qualtrics, an online data collection platform. Only those participants who were scheduled to complete the 14 th -day follow-up survey for the second dose according to the recommended interval between the two doses were included in the analysis. Participants could withdraw from the study anytime. † Self-reported adverse reactions include local (numbness, soreness, pain, swelling, redness, and itch), systemic (sore throat, tiredness, fever, chills, sweating, cough, headache, muscle pain, joint pain, pain in limbs, abdominal pain, diarrhea, nausea, vomiting, poor appetite, insomnia, feeling unwell, enlarged lymph nodes, rash, and temporary one-sided facial drooping), and severe allergic reactions (hypotension, dizziness, itchy skin rash, swelling of face or tongue, and wheezing/shortness of breath). ‡ Person-level covariates include sex, educational attainment, number of chronic medications, and a range of specified chronic conditions, namely autoimmune diseases (ankylosing spondylitis, psoriasis, rheumatoid arthritis, systemic lupus erythematosus), cancer (both remission and under treatment), respiratory diseases (asthma, chronic obstructive pulmonary disease, and others), and other common chronic illnesses, including hypertension, hypercholesterolemia, heart disease, diabetes, stroke, neurological disorders, mental health disorders, liver problems, and kidney problems. At the measurement level, specific follow-up days (vaccination day, first-, second-, third-, seventh-, and fourteenth-day after vaccination) of both doses were also adjusted for given the anticipated day-dependent reactogenicity. and also received speaker fees from Janssen and Medice in the previous 3 years. EWYC 

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